The present invention relates to a piston for an internal combustion engine and, more particularly, to a piston having improved heat resistance.
Recently, piston heat load has become more severe as improvement in performance occurs in internal combustion engines. Particularly, the heat load is great during engine operation at high speed under partial load, and abnormal combustion or detonation tends to occur. Abnormal combustion is generated by self ignition at the piston top at high temperatures prior to, or simultaneously with, ignition by the ignition plug in the compression stroke, causing roughness of the surface of the piston head. Abnormal combustion tends to occur particularly at the squish area, and accordingly, the roughness of the surface so-created adversely effects engine performance.
To protect the piston head, it has been proposed that the piston head be covered with an iron plated layer (Japanese Utility Model Laid-Open Publication No. 57-28147) or a nickel plated layer (Japanese Patent Laid-Open Publication No. 55-78856), for example.
Although damage to the piston head due to abnormal combustion is eliminated by forming such plated layers on the piston head, another problem exists. That is, the improvement in heat resistance of the piston head has permitted the us of the piston under even more severe thermal conditions. As a result, where measures to provide heat resistance have not been taken, surface roughening due to high temperature is generated between the topmost of the piston rings and the groove for receiving the top ring. Consequently, the top ring cannot perform adequately.
Accordingly, it is an object of the present invention to provide a piston for an internal combustion engine which eliminates surface roughening at the top of the piston and at the top ring groove, thereby rendering the piston applicable to high-output engines subject to high combustion temperatures.